The present invention relates to inkjet printing apparatuses, and particularly to inkjet printheads.
An inkjet printhead generally has an ejector chip, such as a heater chip. The heater chip typically includes logic circuitry, a plurality of power transistors, and a set of heaters or resistors. A hardware or software printer driver will selectively address or energize the logic circuitry such that appropriate resistors are heated for printing. For example, when the resistors are heated, the temperature of the resistors is raised, and the ink is subsequently vaporized and ejected from the nozzles as ink droplets. To assure good print quality, it is important to accurately eject a precise amount of ink. In order to effect this goal, the temperature at the printhead has to be monitored and controlled.
Various techniques are used to measure the heat generated by or the temperature of the resistors during printing operation. For example, some printheads position a temperature sense resistor (“TSR”) near the heaters on a substrate such that the TSR can sense or detect the temperature of the heaters. The TSR is typically grounded at the heater chip, which is connected to the substrate of the printhead. The heater chip ground potential may fluctuate with respect to the voltage of the TSR during printing, which results in a ΔV (i.e., a voltage shift between ground of the printer and the ground of the printhead). While the TSR can measure a heater temperature that ranges in a few mV per ° C., the ΔV caused by the ground fluctuation may create a noise as high as 200 mV per ° C. The amplitude of the noise is much greater than the signals to be measured, is difficult to filter, and may affect the overall accuracy of the temperature measurement. Any inaccuracy may lead to inadequate control of the heaters, which in turn may result in poor print quality.